Hello, Welcome to HCM, I am Dr. Das.
Look, thyroid is a mysterious gland. In autoimmune diseases like hushimoto's thyroiditis, body develops antibodies against the thyroglobulin
, thyroid peroxidase
. This leads to destruction of the thyroid gland. It causes release of the residual hormone in blood. So, in this period, patient will present with features of hyperthyroidism
. But, when the residual hormone is finished, then there is low thyroid hormone level leading to features of hypothyroidism
So, this is the problem in very simple word.